1. Field of the Invention
The present invention relates to a method for manufacturing improved regenerated cellulose fiber with improved swelling in water and fibrillation character, which are intrinsic defects of regenerated cellulose fiber, together with superior handling. Improved regenerated cellulose fiber obtained by the present invention is utilized in wide application fields as yarn, woven and knitted fabrics, non-woven fabric and paper, exhibiting these performances.
2. Description of the Related Art
Regenerated cellulose fiber such as rayon and polynosic is composed of cellulose like natural fibers such as cotton and hemp, and has been an indispensable material in clothing field thanks to its superior moisture absorbing property and biodegradability. However, regenerated cellulose fiber, in particular rayon, has defects of poor stiffness and resilience, although superior in soft handling and draping. In addition, it has further defects such as poor water resistance leading to high degree of swelling in water and shrinkage percentage after washing and whitening due to fibrillation. Polynosic fiber have been developed to largely improve these properties of rayon and attained a certain level of improvement. However, the fiber is not sufficient in water resistance and stiffness compared with natural cellulose fibers such as cotton and hemp.
In order to eliminate these defects, treatments of regenerated cellulose fiber with a crosslinking agent have been tried since before. JP-A-59-94681, for example, discloses a method for crosslinking treatment of woven and knitted fabrics containing cellulose fiber with an epoxy crosslinking agent to obtain wash-and-wear and crease resistant characters. JP-B-10-237765 also discloses a method for improving handling by treating an artificial cellulose fiber or it""s fabric with polyethylene glycol and an epoxy compound. However, in crossliking of regenerated cellulose fiber, treatment with a crosslinking agent after formation of cellulose fiber leads to a formation of crosslinks only in the vicinity of fiber surface because crosslinking agent hardly penetrate into an inner part of the fiber, and it results in an insufficient suppression of degree of swelling in water and a poor stiffness in physical properties, although fibrillation can be certainly suppressed.
JP-A-9-170126 discloses a method for a heat treatment of cellulose fiber yarn after contacting with formaldehyde vapor. This method enables a hydrophobic crosslinking agent of low molecular weight such as formaldehyde to penetrate into a fiber to form crosslinks in an inner part of a fiber, and thus to reduce fibrillation, suppress swelling and improve crease resistance. However, the method has defects such as reduction of moisture absorption which is an intrinsic superior performance of regenerated cellulose fiber, and lowering of strength. Use of increased amount of a crosslinking agent to improve degree of swelling and physical properties may attain improvement of degree of swelling, but is apt to cause defects such as stiffening of fiber, lowering of fiber strength and facilitated fibrillation.
As a method to promote a reaction of a crosslinking agent inside a fiber by performing the reaction during formation of a regenerated cellulose formed product, JP-A-11-187871, for example, discloses a method to drop a viscose solution into a coagulation bath then take out it and react with a crosslinking agent before completion of coagulation and regeneration. This method needs to take out a formed product in the way of coagulation in order to promote a reaction with a crosslinking agent inside a fiber. Thus, in an application to a fiber, it is difficult to apply to polynosic, although applicable to rayon with a skin-core structure. Furthermore, it is not practical to be applied to a continuous production process particularly for fiber, due to a difficulty in controlling a coagulation process.
Object of the present invention is to provide a method for manufacturing improved regenerates cellulose fiber having reduced swelling in water, which is a defect of regenerated cellulose fiber, and superior handling, along with suppressed generation of fibrillation, by eliminating the defects described above.
Another object of the present invention is to provide an improved regenerated cellulose fiber and products obtained therefrom.
The inventor, after thorough studies to solve the defects described above, found out that fibrillation, swelling in water, shrinkage percentage after repeated washings and low stiffness, which were big defects of regenerated cellulose fiber, could be improved without reductions of strength and moisture absorption or deterioration in handling, by adding a crosslinking agent to a cellulose viscose solution then extruding the solution into a coagulation and regeneration bath, or by treating with a crosslinking agent solution again after spinning similarly as described above, and thus reached the present invention.
The present invention is a method for manufacturing improved regenerated cellulose fiber, by adding a crosslinking agent having two or more reactive functional groups in a molecule to a cellulose viscose solution and mixing, then extruding the viscose solution into a coagulation and regeneration bath, followed by applying a heat treatment. The present invention is also a method for manufacturing improved regenerated cellulose fiber, by adding a crosslinking agent having two or more reactive functional groups in a molecule to a cellulose viscose solution and mixing, then extruding the viscose solution into a coagulation and regeneration bath, followed by contacting thus obtained regenerated cellulose fiber with an aqueous solution of a crosslinking agent having two or more reactive functional groups in a molecule then applying a heat treatment. The present invention is further a method for manufacturing improved regenerated cellulose fiber, wherein the crosslinking agent used is an epoxy-based crosslinking agent, and still further a method for manufacturing improved regenerated cellulose fiber, wherein the amount of a crosslinking agent added to a cellulose viscose solution is 1-15% by weight to cellulose in a cellulose viscose solution. The present invention is furthermore a methods for manufacturing improved regenerated cellulose fiber, wherein the concentration of an aqueous solution of a crosslinking agent to be contacted with regenerated cellulose fiber after spinning is 1-10%.
Moreover, the present invention is a method for manufacturing improved regenerated cellulose fiber, wherein fine particles of mixed-in additives are added to a cellulose viscose solution and mixed in addition to a crosslinking agent, and furthermore is a method for manufacturing improved regenerated cellulose fiber, wherein the said mixed-in agent described above is fine granular chitosan.
Furthermore, the present invention is an improved regenerated cellulose fiber and products obtained therefrom.
A crosslinking agent added to a cellulose viscose solution in the present invention is a compound having two or more reactive functional groups in a molecule, and preferably the reactive functional groups are glycidyl ether group or chlorohydrin group. Typical examples include those having two or more reactive functional groups in a molecule comprising ethyleneglycol types such as ethyleneglycol diglycidyl ether and polyethyleneglycol diglycidyl ether and propyleneglycol types such as propyleneglycol diglycidyl ether and polypropyleneglycol diglycidyl ether and the like. Epoxy-based crosslinking agents having three or more reactive functional groups such as glycerol glycidyl ether may also be used without any problem. Chlorohydrins before cyclization to epoxy compounds may also be used as a crosslinking agent of the present invention without any problem because these compounds are immediately cyclized to epoxy compounds due to an action of sodium hydroxide contained in a cellulose viscose solution in high concentration when added to a cellulose viscose solution. And the crosslinking agent used may be selected alone among the compounds described above or as a mixture of two or more thereof.
In a method for manufacturing improved regenerated cellulose fiber of the present invention, a spinning stock solution is prepared by adding a crosslinking agent described above to a cellulose viscose solution prepared in advance so that the concentration becomes 1-15% by weight to cellulose in the cellulose viscose solution, followed by mixing homogeneously. The concentration less than 1% by weight is not preferable due to little suppression effects on swelling in water, while the concentration higher than 15% by weight is not preferable due to lowering in physical properties of fiber such as strength.
Concerning a method for adding a crosslinking agent, a crosslinking agent, when it is water soluble, may be added simply to a cellulose viscose solution right before spinning or spinning may be performed after an agitation for a predetermined period after the addition. However, in using crosslinking agents of ethyleneglycol type with a high solubility in water, an attention should be paid to avoid leaking out of the agent into a coagulation and regeneration bath. In this case, the leaking out of the crosslinking agent into a coagulation and regeneration bath can be avoided, for example, by agitating for some period after the addition of the crosslinking agent to a viscose solution. Crosslinking agents of propyleneglycol type with a less solubility in water can be suitably used without leaking out into a coagulation and regeneration bath, even if they are added right before spinning. Moreover, crosslinking agents with a low or substantially little solubility in water may be added and mixed in an usual way, or preferably added as a dispersed solution to a cellulose viscose solution by dispersing with a dispersing agent such as surfactant in advance from the view point of a reactivity of the crosslinking agent. Furthermore, concerning a timing of addition in the case of hydrophobic crosslinking agents, they may be added to a cellulose viscose solution in advance or right before spinning.
In the present invention, in order to exhibit functions such as antibacterial activity, deodorizing property and dyeability, for example, fine particles of mixed-in additives such as fine granular regenerated chitosan, hollow fine particles and anionizing agent can be jointly used in addition to titanium dioxide as a dull agent usually used when the crosslinking agent described above is added.
Regenerated cellulose fiber is manufactured by spinning the spinning stock solution described above. Spinning conditions in this process are not specifically restricted, and the usual conditions to obtain regenerated cellulose fiber may be used.
Regenerated cellulose fiber obtained by spinning and scouring is then applied with a heat treatment to promote sufficienlty the reaction of a crosslinking agent contained in a fiber so that crosslinks are formed even at the central part of a fiber to obtain an improved regenerated cellulose fiber. Any condition of the heat treatment may be applicable so long as the reaction of a crosslinking agent is sufficiently performed, and typically, a condition, for example, at 130xc2x0 C. for 15 min. is sufficient.
The process for manufacturing improved regenerated cellulose fiber of the present invention mentioned above can improve characteristics such as swelling in water and low stiffness, which are defects of regenerated cellulose fiber, without impairing superior properties intrinsic to regenerated cellulose fiber, due to a homogeneous formation of crosslinking between cellulose molecules by reacting a crosslynking agent contained in a fiber in an inner part of a fiber.
Furthermore, in the present invention, as described above, regenerated cellulose fiber obtained by adding a crosslinking agent to a cellulose viscose solution and mixing, is further applied with a crosslinking agent solution treatment and a heat treatment after a scouring process to suppress generation of fibrillation. The latter crosslinking agent may be an epoxy-based agent similar to the agent added to a viscose solution described above, and it may be the same to or different from that added to a stock solution. When a crosslinking agent has a low solubility in water, it may be dispersed using a dispersing agent such as surfactant. When chlorohydrin is used, a pretreatment for cyclization is necessary by adding an equivalent mole of sodium hydroxide. In this case, the concentration of crosslinking treatment is preferably performed with 1-10% aqueous solution of the crosslinking agent. The concentration of the crosslinking agent less than 1% is not preferable due to little effect on crosslinking to suppress fibrillation, while the concentration higher than 10% is not preferable due to an excessive crosslinking resulting in a hardened fiber surface and instead more easy fibrillation.
An improved regenerated cellulose fiber is obtained by applying a heat treatment followed by washing and drying, and the conditions of the heat treatment are desirably at 130xc2x0 C. for 15 min. to perform the crosslinking treatment completely.
The process for manufacturing improved regenerated cellulose fiber of the present invention can improve characteristics such as fibrillation, swelling in water and low stiffness, which are defects of regenerated cellulose fiber, without impairing superior properties intrinsic to regenerated cellulose fiber, due to a homogeneous formation of crosslinking by reacting a crosslinking agent contained in a fiber in an inner part of a fiber, followed by promoting further crosslinking reaction at a fiber surface.
According to the present invention the improved regenerated cellulose fibers provide improvements in swelling in water, shrinkage percentage after washing and stiffness in handling, which are defects of regenerated cellulose fibers, without impairing a high moisture absorption or a flexibility both intrinsic to regenerated cellulose fibers, along with eliminating defects such as an easy generation of fibrillation. By these improvements, the present invention enables regenerated cellulose fibers to spread to various fields which have been unsuitable for regenerated cellulose fiber until now. The present invention also provides an enhancement in added value by adding fine particulates of mixed-in additives having functions such as antibacterial activity and deodorization together with the crosslinking agent to a spinning stock solution.